The present invention relates to a communication controlling apparatus for a single-line telephone with extensions thereto, especially one which allows an external call to be received when two extension telephone sets are in communication.
Telephone communication is used popularly in nearly every family at the present time. Most families have installed extension telephone sets in different rooms. However, persons in different rooms can not have a convenient communication using the extension telephone sets, because a busy tone will be heard in each extension telephone set when the persons communicate with each other. Moreover, an external call can not come in when the persons are using the very inconvenient extension telephone sets to have an intercom telephone communication. Therefore, it is requisite to provide a communication controlling apparatus which allows people in different rooms of a house to use extension telephone sets to communicate with each other and also allows an external call to come in.